esxcfg-nics -l and esxcli network nic list are two CLI commands that can be used to see the vmnic link status on an ESXi host. Both commands display information such as the vmnic name, driver, link state, speed, and duplex mode. The link state can be either Up or Down, indicating whether the vmnic is connected or not. For example, the output of esxcfg-nics -l can look like this:
Name PCI Driver Link Speed Duplex MAC Address MTU Description
vmnic0 0000:02:00.0 igbn Up 1000Mbps Full 00:50:56:01:2a:3b 1500 Intel Corporation I350 Gigabit Network Connection vmnic1 0000:02:00.1 igbn Down 0Mbps Half 00:50:56:01:2a:3c 1500 Intel Corporation I350 Gigabit Network Connection